Thermionic valve circuits



Oct. 23, 1951 E. L. c. WHITE 2,572,792

THERMIONIC VALVE CIRCUITS Original Filed Aug. 5, 1947' 70M /7/V P077 or 62 /95 0; 54 55 MAI/5 51555 CO/VMOL P07. v

INVENTOR [WC ZIWEQVCE Gift/N6 W/l/fE A TORNEY Patented Oct. 2 3, 1951 THERMIONIC VALVE CIRCUITS Eric Lawrence Casling White, Iver, England, as-

signor to Electric 8; Musical Industries Limited, Hayes, England, a company of Great Britain Original application August 5, 1947, Serial No. 766,318 Divided and this application August 23, 1950, Serial No, 180,927. In Great Britain April 24, 1946 10 Claims.

This invention is a division of the copending application, Serial No. 766,318, filed August 5, 1947.

This invention relates to modulating circuit arrangements of the kind comprising a pair of thermionic valves having their cathodes connected to a common cathode impedance.

In circuits of this kind, if a signal is applied to the control electrode of one of said valves while the control electrode of the other valve is maintained at a relatively fixed potential, or if a' si nal is applied in push-pull to the control electrodes of the respective valves, a signal corresponding to the difference of potential of the two control electrodes will appear in each anode circuit. The am litude of this signal will depend, apart from the constant circuit parameters, on the amplitude of the input signal and the mutual conductance of the combination of valves. The mutual conductance will in turn depend mainly on the mean cathode current of the valves, and by varying the mean cathode current, modulation of the signal in the anode circuits will occur.

An object of this invention is to provide an improved circuit in which modulation is efiected in this way.

According to the present invention there is provided a circuit arrangement of the kind described comprising a modulating valve whose anode-to-cathode path is connected in series with the cathodes of the valve pair so that the anode current of said modulating valve serves to modu late the valve pair at their cathodes.

According to another feature of the invention, there is provided a circuit arrangement of the kind described wherein a modulating valve is provided whose anode-to-cathode path is connected in series with the cathodes of said valve pair, and wherein modulating signals independent of signals derived from said valvepair are-applied to the control electrode of said modulating valve so that the anode current of said modulating valve serves to modulate said valve pair at their cathodes.

The modulating valve thus constitutes part at least of said common cathode impedance. A modulating signal applied to the control electrode of the modulating valve will vary the meancathode current of the valve pair, since this cathode current is the anode-currentofthe modulating valve, thus producing the desiredmod-ulation.

According .to the present invention',-there is provided a circuit arrangement of the =kinddescribed in which the control electrode-to-cathode (Cl. 332E553) circuits of each of the pair of valves include as a part thereof the anode-cathode path of the modulating valve. Modulating signals are applied to the control electrode of the modulating valve. A

voltage to be amplitude modulated is applied to the control electrode of at least one of the pair of valves (which have their cathodes connected to a common cathode impedance).

A circuit of the above-described type may be employed to generate deflecting potentials for application to the deflecting plates of a cathode ray tube.

Another application to which the invention can be put is channel fading or switching, such as the prising in this case a further triode 2 ll whi ch constitutes a modulating valve or electron discharge device. The device 20 has its anode:- catho'de path in series with the cathodes of the pair of devices I! and I8. Thus, the anode :cur-. rent .of the'valve 20 is arranged to modulate'tlie valves l1, It at their cathodes.

Two sources of direct potential] and 2, illus-' trated asbatteries, are connected in series aiding relationship and the common junction thereof is grounded. The ungrounded or positive end of source I is connected through suitable separate load resistors to the anodes of tubes I1 and 8;. The ungrounded or negative end of source 2 is connected through a resistor to the cathode of modulating tube 20. The cathodes of tubes H to the intermediate grounded point between sources and 2. Thence, toget tothe cathode of valve l1,vve go through source land-the cathode-anode pathof tube 20. Therefore,the control-electrode toecathode circuit of device 11 in-. cludes as a part thereof thecommoncathode impedance 20, or the anode-cathode path of modulating device 20.

The control electrode of valve I8 is connected directly to ground. Thence, to get to the cathode of valve I8, we go through source 2 and the cathode-anode path of tube 20. So, the control electrode-to-cathode circuit of device I8 also includes as a part thereof the common cathode impedance 20, or the anode-cathode path of modulating device 20.

By means of the above-described connections, the modulating valve 20 is included in the control electrode-to-cathode circuits of valves I1 and I8, as well as in the anode-cathode circuits of such valves. Therefore, any potential variation set up at the anode of modulator valve 26-will be efiective to modulate the potential between the control electrodes and cathodes of the pair of valve I'i, I8. This is, of course, in addition to the potential variation, between the anodes and cathodes of the modulated valves I1 and I8, produced by potential variation set up at the anode of valve 26. The present invention constitutes a substantial improvement over the so-called anode modulated or series modulator arrangements of the prior art (in which only anode-cathode potential variations are produced in the modulated valves), since it is much more sensitive than such prior art arrangements and is capable of giving more linear modulation.

The circuit arrangement illustrated in Fig. 1 is employed to generate deflecting potentials for application to the deflecting plates of a cathode ray tube for deflecting the electron beam therein, the circuit being arranged to generate two pairs of potentials one of which is so modified with respect to the other, that the mean potential of the former pair is lowered below the mean potential of the latter pair by an amount effectively proportional to the difference between the potentials of the former pair. The potentials of the latter pair are generated at the anodes of valves I and I6, while the potentials of the former pair are generated at the anodes of valves I1 and I8. The two valves I5 and I6 have a common cathode resistance I9 while the two valves I1 and I8 have a common cathode impedance which comprises valve 26. A linear sawtooth potential is applied to the control electrodes of the valves I5 and I1 through a coupling capacity 2| and resistance 22 so that due to the provision of the cathode resistance I9 a pair of push-pull potentials is generated at the anodes of valves I5, I6 and another pair of push-pull potentials is generated at the anodes of valves I], I8. The latter potentials are, however, modified with respect to the potentials generated at the anodes of the valves I5 and I6 by reason of modulating signals applied to the control electrode of the modulating valve 20. The control electrodes of valves I6 and I8 are grounded, as is also one of the input terminals. The control electrodes of the valves I6 and I8 are shown grounded but if potentials such as applied to the control electrodes of valves I5 and H are available in push-pull, they can be applied to the control electrodes of each pair of valves I5, I6 and I1, I8.

The cathodes of tubes I5 and I6 are connected together and through resistor I9 to the negative or ungrounded end of source 2. The anodes of tubes I5 and I6 are connected through separate anode load resistors to the positive or ungrounded end of source I. An output may be taken, as shown, from the anode load resistors of valves I5 and I6.

The other output, as previously stated, is taken from valves I! and IS.

The modulating signal which is applied to the control electrode of the valve 20 is obtained from the sawtooth potential applied to the control electrodes of the valves I5 and I1, the potential being however integrated via a resistance 23 and condenser 24 before being applied via a coupling con denser 25 and resistance 26 to the control electrode of the valve 20. The time constant of the resistance 23 and condenser 24 is made much greater than the period of the sawtooth potential applied to the control electrode of the valves I5 and I1, and by integrating the applied sawtooth potential the current passed by the valve 20 is caused to vary in an effectively parabolic manner, and by a suitable choice of components it is possible to arrange that the mean of the potentials at the anodes of the valves I'I, I8 is lowered below the mean of the potentials at the anodes of the valves I5, I6 by an amount effectively proportional to the square of the difference of the potentials at the anodes of the valves II, I8. If desired, instead of the resistance 23 being connected to the control electrodes of the valves I5 and I! and thus directly to the input potential, it may with advantage be connected to the anode of valve I6, where the amplified sawtooth waveform is in a positive sense. This may be done if the amplitude of the sawtooth waveform applied to the circuit is insufiicient to cause operation in the required manner.

Another application to which the invention may be put is channel fading or switching when it is desired for example to switch out the output of one channel progressively from a transmitter, while progressively switching in the output of another channel, and a circuit such as shown in Fig. 2 may be employed for this purpose. It is assumed that one set of intelligence signals is fed along the channel 41 and another set of intelligence signals is fed along the channel 48, the signals being applied to the control electrodes of the valves, and the circuit enables the signal in either channel 41 or channel 48 to be fed to a signal output channel 49 common to the channels 41 and 48. The output of the channel 41 is applied to the control electrode of a valve 5!] while the signal output channel 49 is connected to the anode of a valve 5|, these valves corresponding to the valve I'I, I8 in for example the circuit of Fig. l. The output of the channel 48 is similarly applied to the control electrode of a valve 52 andthe signal output channel 49 is connected to the anode of another valve 53, the valves 52, 53 comprising another valve pair corresponding to the valves I1, [8. The control electrodes of the valves 50 and 52 are connected, via a suitable resistance 3, to a common point on a potential source 60 at which a relatively fixed potential is available equal, say, to the mean potential of the control electrodes of the valves 5I and 53. The valves Hand 50 have a modulating valve 54 connected in their cathode circuit, and the valves 52, 53 have a second modu lating valve 55 connected in their cathode circuit, the valves 54, 55 having in turn a common cathode impedance 56, and having their control electrodes comiected via resistances 6 and I to a suitable point on a potential divider across the source 60 of negative potential, which is applied to the cathodes of the valves 54, 55 via the impedance 56. The signal output channel 49 feeds into a cathode follower valve 51, the valve 51 feeding the output to channels 58.

In Fig. 2, as in Fig. 1, the control electrode-tocathode circuits of devices 50 and 51 include as parts thereof the common cathode impedance represented by modulating device 54. From the control electrode of tube 50, we go through a portion of resistor 3 to the tap thereon. Thence, to get to the cathode of valve 50, we go through part of source 60, resistor 56, and the cathode-anode path of tube 54. The control electrode-to-cathode circuit of device 5! may be traced as follows: control electrode of tube 5|, point 4, resistor 5, ground, source 60,, resistor 56, cathode-anode path of tube 54, cathode of tube 5|.

Similarly, the control electrode-to-cathode circuits of devices 52 and 53 include as parts thereof the common cathode impedance represented by modulating device 55. The control electrode-to-cathode circuit of device 52 may be traced as follows: control electrode of tube 52, part of resistor 3, midtap of resistor 3, part of source 60, resistor 56, cathode-anode path of tube 55, cathode of tube 52. The'control electrode-tocathode circuit of device 53 may be traced as follows: control grid of tube 53, point 4, resistor 5, ground, source 60, resistor 56, cathode-anode path of tube 55, cathode of tube 53.

By applying appropriate potentials to the control electrodes of the valves 54 or 55, switchin from channel 41 to channel 48 or vice versa can be effected in a variety of ways. For example, assuming the channel 41 is feeding signals to the output channel 49, in which condition the valve 54 is conducting and the valve 55 non-conducting, and a progressively increasing negative bias potential is applied to the control electrode of the valve 54 until this valve is biased beyond out off and the bias potential applied to the control electrode of the valve 55 is simultaneously varied in the opposite sense, the signals in channel 4'! will be gradually faded out from the channel 49, while the signals in channel 48 are being fed into channel 49 with increasing amplitude. The variation of the bias potentials applied to the control electrodes of valves 54 and 55 may be effected by means of potentiometers operated by means of a single control knob. A third pair of valves may, be provided, and the output channel 49 connected to the anode of one valve of this third pair, the control electrode of the other valve of this third pair being maintained at a relatively fixed potential. In this case a third modulating valve is connected in the cathode circuit of the third pair of valves, the cathode of the modulating valve being in turn connected to the impedance 56, and further potentiometers are provided, one for the control electrode of each modulating valve ar ranged so that when switching is effected one of the valves 54, 55 is biased beyond cut ff before the other valve is rendering conducting. the third modulating valve becoming conducting during the interval when both the valves 54 and 55 are nonconducting. As a result, the intelligence signals in one channel are cut off from the output channel 49 completely and an interval is caused to occur before the second set of intelligence signals is switched into the channel 49. The said further potentiometers may be operated by the same control knob as thefirst-mentioned potentiometers, a selector switch being provided under the control of the operator which can be pre-set to cause the control knob to operate the desired set of potentiometers when switching from one channel to the other is next effected.

What I claim to be my invention is as follows 1. A circuit arrangement, comprising a pair of electron control devices each having a control electrode and a cathode, a direct connection denection devoid of concentrated impedance between the anode of said modulating device and said first-named direct connection, said modulating device having a control electrode, and means for applying modulating signals to said last-named control electrode to thereby modulate the current in said pair of control devices.

2 A circuit arrangement as defined in claim 1, wherein means are provided for applying energy to be modulated to the control electrode of one of the control devices.

3. A circuit arrangement, comprising a pair of electron control devices each having a control electrode and a cathode, a common cathode im-v pedance connected to the cathodes of both said devices, control elec-trode-to-cathode circuits for each of said devices, each of said circuits includ-. ing as a part thereof said impedance, said impedance comprising the anode-cathode path of a modulating electron discharge device connected; in series with the pair of control devices, said discharge device having a control electrode, means for applying energy to be modulated to the con-- trol electrode of one of the control devices, and means coupled to said last-named means for integrating some of said energy and for applying the integrated energy to the control electrode of said discharge device as a modulating signal therefor.

4. A circuit arrangement, comprising a plurality of pairs of electron control devices each device having a control electrode and a cathode, a like plurality of common cathode impedances each connected to the cathodes of both devices of a corresponding pair of devices, control electrodeto-cathode circuits for each of said devices, the circuits of both devices of each pair of devices including as a part thereof the corresponding impedance, each of said impedances comprising the anode-cathode path of a modulating electron discharge device connected in series with its corresponding pair of control devices, each of said discharge devices having a control electrode, each of said pairs of control devices having an output channel in common with the output channels of the other pairs of devices, and means for applying signals to the control electrodes of said modulating devices to open the anode-cathode paths of all of said modulating devices except one and to close the anode-cathode path of said last-named one modulating device.

5. A circuit arrangement in accordance with claim 4, wherein means are provided for applying a separate signal to be switched to the control electrode of one control device of each pair of devices.

6. A circuit arrangement, comprising a pair of tubes each having an anode, a cathode and a control electrode and each having an anode-cathode circuit, a third tube having an anode, a cathode and a control electrode and having a cathodeanode space discharge path common to the anodecathode circuits of said pair of tubes, means coupled to the control electrode of one of said pair of tubes for integrating signals applied to said lastmentioned electrode. and means coupled to said last-mentioned means and to the control electrode of said third tube for applying the integrated signal to such electrode.

7. A circuit arrangement in accordance with claim 6, wherein the signals applied to the control electrode of said one of said pair of tubes constitute energy to -be modulated by potential variations set up at the anode of said third tube.

8. A circuit arrangement, comprising a plurality of pairs of tubes each tube having an anode, a cathode and a control electrode and each having an anode-cathode circuit, a like plurality of modulating tubes each having an anode, a cathode and a control electrode and each having a cathode-anode space discharge path, the space discharge path of each of said modulating tubes being common to the anode-cathode circuits f the two tubes of a corresponding pair of tubes, each of said pairs of tubes having an output channel in common with the output channels of the other pairs of tubes, and means for applying signals to the control electrodes of said modulating tubes to open the cathode-anode space discharge paths of all of said modulating tubes except one and to close the cathode-anode discharge path of said last-named one modulating tube.

9. A circuit arrangement in accordance with claim 8, wherein means are provided for applying a separate signal to be switched to the control electrode of one tube of each pair of tubes.

10. A circuit arrangement, comprising a pair of electron control devices each having a control electrode, a'cathode and an anode, a direct connection devoid of concentrated impedance between the two cathodes, a common cathode impedance connected to the cathodes of both said devices, control electrode-to-cathode circuits for each of said devices, each of said circuits including as a part thereof said impedance, said impedance comprising the anode-cathode path of a modulating electron discharge device connected in series with the pair of control devices, there being a direct connection devoid of concentrated impedance between the anode of said modulating device and said first-named direct connection, said modulating device having a control electrode, means for applying modulating signals to said last-named control electrode to thereby modulate the current in said pair of control devices, a source of repetitive waves connected to the control electrode of one device of said pair of devices, and an output circuit connected to the anode of said device of said pair of devices.

ERIC LAWRENCE CASLING WHITE.

Name Date Usselman Oct. 6, 1942 Number 

